Project Summary. The Center for the Study of Tobacco Products (CSTP) has developed a model for evaluating novel tobacco products using, as exemplars, electronic cigarettes (ECIGs) that heat a liquid that often contains nicotine, forming an aerosol that users inhale. Now, CSTP leverages its methodological and ECIG expertise to pivot from product evaluation to an integrative theme of impact analysis. Specifically, the CSTP proposes methods with which FDA can generate predictions regarding a potential regulation?s effects, and then whether or not the predicted effects occur in the population can be tested. The CSTP?s model assesses how potential regulation might influence product toxicity (Project 1), user behavior (Project 2), and product addiction/abuse liability (Project 3) and, together, these projects will contribute to predictions regarding population-level phenomena. Project 4 will test the validity of those population-level predictions. FDA regulations are intended to promote health, but also may have unintended consequences. For example, limiting ECIG liquids to <20 mg/ml nicotine, as in the European Union (EU), can drive use of high power ECIGs that aerosolize more liquid, leading users to inhale more nicotine. Unintended consequences may also occur from other action, such as constraining ECIG nicotine flux (emitted nicotine/unit time), or reducing flavor availability. Examining how these and other potential regulations influence product toxicity, user behavior, and product abuse liability in controlled settings can lead to predictions regarding population-level consequences. However, the accuracy of these predictions should be tested. Population-level effects of tobacco product regulation can be measured after the regulation is put into place using large-scale longitudinal surveys. Project 4 specific aims are to test population-level predictions that arise from Project 1-3?s controlled studies of product toxicity, user behavior, and product abuse liability using a prospective cohort survey that includes current exclusive ECIG users (N=600) and current dual users of ECIGs and tobacco cigarettes (N=600). Specifically, the study will assess the population-level effects of three potential regulatory actions: (1) limits on nicotine, (2) constraints on nicotine flux, and (3) reduction in flavor availability. Project 4 addresses the scientific domain of impact analysis and its instruments are informed by the Contextual Knowledge Core that will help determine how to assess self-report accurately and assess dependence reliably among ECIG users. Overall, results will reveal the extent to which observations made under controlled conditions yield valid population-level predictions. Thus, this project is part of a center with an integrative theme of impact analysis that draws on the team?s expertise in evaluating population-level effects of tobacco regulation and will provide FDA a set of tools that can be used to guide regulation development so that, by the time a regulation goes into effect, validated methods have been used to test it, refine it, and generate data that show that its health-promoting effects are maximized and unintended consequences are minimized.